The truck had gone off the road and into the gorge, and emergency services were notified at 5.30am when another truck driver drove out of the gorge into cellphone range and raised the alarm.

The road might be closed temporarily while cranes lifted the truck from the river, and motorists could expect some delays.

Waikato Regional Council emergency response manager Rob Dragten said the truck was taking evaporated whey protein, a product of cheese making, from Lichfield to Kapuni for further processing or disposal.

He said the sticky, sweet protein was leaking into the Awakino River.

‘‘Because this material is high in sugar it breaks down in water quickly and reduces the amount of oxygen in the river.’’